Because of the recent increase in fuel prices, the priceof food is more expensive than before.

This is obviously a direct translation of harganya lebih mahal!

This is really a collocation problem. The IELTS examiner will understand what you mean, but you will not receive a good score for vocabulary. A product or service can be expensive, but the price of the product or service is either high or low.

More correct collocation is as follows:

Because of the recent increase in fuel prices, theprice of food is higher than before.

Because of the recent increase in fuel prices, food is more expensive than before.